The effect of X-point tunneling in AlAs-GaAs-AlAs double barrier heterostructures is studied numerically and experimentally. Numerical simulations are performed within the framework of the one-band Wannier orbital model, which allows for simulatneous descriptions of the Γ-point double barrier profile and the X-point double well profile. This model is used to illustrate the dynamics of the following processes: resonant tunneling via the X-point quasi-bound states, non-resonant tunneling through X-point continuum states, and resonant tunneling through Γ-X mixed quasi-bound states. X-point effects on the tunneling escape times of electrons initially localized in the GaAs quantum wells are examined theoretically, and found to be supported by the observation of a dramatic drop in the Γ-point-related quantum well photoluminescence intensity.

The strain configuration in CdTe/ZnTe strained-layer superlattices has been measured by Raman scattering near resonance. The ZnTe-like longitudinal optical phonon energy in the superlattice is significantly shifted from the bulk value to lower energies and the shift increases with increasing superlattice CdTe fraction. The observed shifts agree with calculations of strain shifts based on a free-standing strain distribution.

The tunneling time for electrons to escape from the lowest quasibound state in the quantum wells of GaAs/AlAs/GaAs/AlAs/GaAs double-barrier heterostructures with barriers between 16 and 62 Å has been measured at 80 K using photoluminescence excitation correlation spectroscopy. The decay time for samples with barrier thicknesses from 16 Å (≊12 ps) to 34 Å(≊800 ps) depends exponentially on barrier thickness, in good agreement with calculations of electron tunneling time derived from the energy width of the resonance. Electron and heavy hole carrier densities are observed to decay at the same rate, indicating a coupling between the two decay processes.

We have calculated hole tunneling times in GaAs/AlAs double-barrier structures taking quantum well band-mixing effects into account. Our results indicate that for sufficiently high hole temperatures and concentrations, band-mixing effects reduce average hole tunneling times from the pure heavy hole value to values comparable to electron tunneling times in the same structure. For very low hole temperatures and concentrations, band mixing is less important and average hole tunneling times should approach the pure heavy hole value. These results provide an explanation for previously reported experimental results in which electrons and holes were found to be characterized by very similar tunneling times.